The present invention is generally directed to toner compositions and processes thereof, and more specifically, the present invention relates to colored encapsulated toner compositions and processes thereof, and wherein these toners can be directly generated without resorting to the conventional pulverization and classification methods. In one embodiment, the present invention relates to processes for the preparation of colored encapsulated toner compositions comprised of a core comprised of a polymer resin and colorants, including color pigments, dyes, or mixtures thereof, and coated thereover a polymeric shell like a polyurethane shell material. In one embodiment, the present invention relates to processes for preparing encapsulated toners, which process comprises dispersing a mixture of free radical monomer, colorant, or pigment, optionally a charge control agent and containing a shell forming monomer such as dodecane diisocyanate, trimethylhexamethylene diisocyanate and the like in an aqueous medium containing a cellulose surfactant, such as hydroxyethylmethyl cellulose (TYLOSE.RTM.), methyl cellulose and the like; and a dispersant such as sodium dodecylsulfate to control the volume average particle size of from about 3 to about 7 microns in diameter; and adding subsequently a second polymeric stabilizing surfactant, such as polyvinyl alcohol; followed by the addition of a second shell forming monomer, such as an amino terminated propylene glycol (JEFFAMINE D-400.TM. available from Texaco), yielding by polymerization a polyurethane shell; and accomplishing core resin formation step by free radical polymerization. In another embodiment, the present invention relates to a process of preparing colored encapsulated toner of fine particle size of from about 0.5 micron to about 7 microns in diameter and more preferably from about 2 microns to about 7 microns in diameter, as measured by the Coulter Counter. In another embodiment, the present invention relates to colored encapsulated toner compositions which display low fixing temperatures of from about 100.degree. C. to about 120.degree. C., thereby reducing the energy consumption of an electrostagraphic imaging or printing apparatus and prolonging the lifetime of the fuser contained therein. Furthermore, in another embodiment, the present invention relates to a colored encapsulated toner composition and process of generating a polyurethane material surrounding a core material, and wherein the polyurethane material has a softening point of from about 80.degree. C. to about 110.degree. C. as measured by the Shimadzu Flowtester. Additionally, in another embodiment, the present invention relates to colored encapsulated toners which display high projection efficiency of from about 60 percent to about 95 percent transparency as measured by the Match Scan II spectrophotometer available from Milton Roy Corporation. In embodiments, the processes of the present invention can also utilize a combination of cellulose polymers of from about 0.1 percent to about 5 percent by weight of toner, and ionic or inorganic surfactants of from about 0.01 percent to about 0.5 percent by weight of toner, such as potassium oleate, sodium dodecyl sulfate, and the like during the dispersion step. The cellulose-ionic and alkali surfactant system facilitates efficient generation of very small sized microdroplets, particularly those with an average particle diameter of from about 0.5 micron to about 7 microns, together with a narrow particle size distribution of less than 1.35, as measured by the Coulter Counter. The main function of the second surfactant, such as polyvinyl alcohol, selected in effective amounts of, for example, from about 0.1 to about 2 percent by weight of the aqueous fraction and preferably from about 0.5 to about 1 percent by weight of the aqueous portion is to stabilize the microdroplet size such that when the subsequent addition of diamine, such as JEFFAMINE D-400.TM., is employed to form the polyurethane shell, particle coalescence, particle growth or aggregation does not occur, or is minimized.
The primary function of the polyurethane shell of the colored encapsulated toner of the present invention is to provide for the mechanical integrity of toner, minimizing or eliminating the seepage of the inner core material, hence preventing undesired toner aggregation or coalescence. Additionally, another function of the polyurethane shell of the colored encapsulated toner of the present invention, such as that obtained when dodecane diisocyanate and JEFFAMINE D-400.TM. are utilized, is to provide a softening point of from about 80.degree. C. to about 120.degree. C., such that when the aforementioned encapsulated toner is fixed on paper, by the utilization of a hot-roll fusing device, the polyurethane shell melts, deforms or fixes on paper and provides excellent adherence to paper at low minimum fixing temperatures of from about 100.degree. C. to about 120.degree. C., and provides a smooth surface such that when fixed on transparency sheets, results in high projection efficiency.
In color reprography, such as in full color or highlight color applications, colored toners with a wide variety of colors including black are usually employed. In color reprography, a heat-assisted transfix step or heat-roll fusing is applied to the toner image on paper. It is highly desirable to use VITON.RTM. fuser rollers rather than the conventional silicone roll fusers due to the drastically prolonged lifetime attained by a fuser roll containing VITON.RTM. surfaces. During the fixing step employing heated Viton roll fusers, the toner is fixed on paper or transparency, and the energy necessary to achieve this is related to the temperature applied by the rolls. Accordingly, toners which fix on paper with a minimum amount of heat are highly desirable. The temperature necessary to properly fix a particular toner onto paper is known as the minimum fixing temperature (MFT). It is known that encapsulated toner compositions are highly desirable for low minimum fixing applications, such as from about 110.degree. C. to about 150.degree. C., and preferably from about 110.degree. C. to about 130.degree. C. The aforementioned encapsulated colored toners are comprised of a core resin with low glass transition temperature resin enabling, for example, excellent fixing of the toner onto paper at the aforementioned low minimum fixing temperatures. Also, the core is surrounded by a shell material avoiding or minimizing core aggregation or agglomerate during storage or until use. Encapsulated toner fusing onto paper is accomplished by the rupturing of the shell component, release of the sticky inner core resin and its penetration into the paper fiber, and sticking or adherence of the resin onto the paper with colorants, dyes and additives. The primary function of many of the prior art encapsulated toners containing polyurethane shell was for containment of the sticky core resin to avoid toner aggregation. Toner aggregation can result in a dramatic increase of toner particle size, and when transferred electrostatically to paper by various imaging methods results in broad images or undesired low resolution. Accordingly, many prior art encapsulated toners which utilize polyurethane shells rupture during the fixing step and do not melt or adhere to paper, but permit the core binder resin to be released and to fix and adhere onto the paper and to stick or adhere to the ruptured polyurethane component. The aforementioned ruptured shell results in an uneven or bumpy surface texture especially when fused on a transparency causing low projection due to the scattering of light on the toner surface. In color reprography, it is highly desirable to generate process color images on a transparency, which can be used on overhead projectors to project bright colors on wall screens. The quality of the color projection or the percent of transmittance of light through the toner image on the transparency depends on several factors such as acceptable toner pigment dispersion, similar refractive index of shell and core resin, and the surface texture of the toner image whereby surface scattering of light is minimized or eliminated. It is known that bumpy surface texture of toner images on a transparency results in undesired light scattering, hence a low projection efficiency of less than 60 percent transmittance can occur. The encapsulated toners of the present invention in embodiments contains a shell such as a polyurethane shell which is heat fusible, hence melts and softens during the fixing step and is sticky providing excellent adherence to paper or transparency with the core resins such that low minimum fixing temperatures of from about 100.degree. C. to about 120.degree. C. are obtained, thus greatly reducing the energy requirements of the fuser and prolonging its lifetime. Furthermore, the ability of the shell material to soften or melt provides a smooth toner surface and results in low surface scattering, hence a high projection efficiency of from about 60 percent to about 95 percent transmittance as measured by the Match Scan II. Furthermore, the colored encapsulated toners of this invention are of fine average volume particle sizes of from about 0.5 micron to about 7 microns and more preferably from about 2 microns to about 7 microns in diameter. The process for preparing encapsulated colored toners of this invention with average particle sizes of from about 0.5 micron to about 7 microns, utilizes a second surfactant, such as polyvinyl alcohol, which stabilizes the microdroplet and prevents it from coalescing or aggregating during the polyurethane shell forming state. In prior art encapsulated toner processes, a second surfactant to stabilize the microdroplet is not utilized and average particle sizes of from about 0.5 micron to about 7 microns cannot be readily attained, rather average particle sizes of from about 11 microns to about 19 microns are, for example, disclosed. Additionally, the encapsulated toner compositions of the present invention display excellent tribo characteristics such that the triboelectric properties of different colored toners be desirably controlled thus they all can attain similar equilibrium triboelectric charging levels when utilized against a selected carrier. This is especially useful for custom colored toner packages since colored toners with a wide variety of custom colors can be obtained by simple blending of the primary colored toners. Another important aspect for two component development is the rate of charging of the fresh toners to the equilibrium charge levels when they are added to the toner depleted development housing. A fast rate of charging of fresh toner can be important in ensuring proper image development, particularly for high speed, greater than 70 copies per minute for example, reprographic systems.
There was reported in a patentability search relating to encapsulated toners the following prior art: U.S. Pat. No. 5,043,240, the disclosure of which is totally incorporated herein by reference, illustrates a pressure fixable encapsulated toner comprised of a core, and an encapsulating substance comprised of a pressure rupturable shell, wherein the shell is formed by an interfacial polymerization, such as a polyurethane shell, and processes thereof wherein a surfactant stabilizing step prior to the shell formation is not utilized and particle sizes of 13 microns to about 21 microns are reported, however, the process of this '240 patent does not, it is believed, yield toner particles of less than 7 microns, reference Comparative Examples I and II. Furthermore, the polyurethane shell of the aforementioned '240 patent is believed to rupture and may not melt readily resulting in an uneven surface, and hence, display low projection efficieny. The process of the present invention contains a second stabilizer step before formation of the shell resin in order to provide particle stabilization and thus providing small particle sizes of less than or equal to 7 microns in diameter. The utilization of a second surfactant is important in generating small particle size encapsulated toners of less than or equal to 7 microns. Additionally, the polyurethane shell is pressure rupturable and heat fusible, and the monomer components of the polyurethane shells invention include diamino-ethers, such as JEFFAMINE D-400.TM., JEFFAMINE D-700.TM., and the like to enable low softening points of from about 80.degree. C. to about 120.degree. C. such that during the fixing step the polyurethane shell melts, adheres to paper or transparency and provides a smooth toner surface, and hence, high projection efficiency. Other prior art toner patents include U.S. Pat. No. 3,967,962 which discloses a toner composition comprising a finely divided mixture comprising a colorant material and a polymeric material which is a block or graft copolymer, including apparently copolymers of polyurethane and a polyether (column 6), reference for example the Abstract of the Disclosure, and also note the disclosure in columns 2 and 3,6 and 7, particularly lines 13 and 35; however, it does not appear that encapsulated toners are disclosed in this patent; U.S. Pat. No. 4,626,490 discloses an encapsulated toner comprising a binder of a mixture of a long chain organic compound and an ester of a higher alcohol and a higher carboxylic acid encapsulated within a thin shell, reference the Abstract of the Disclosure, for example, and note specifically examples of shell materials in column 8, beginning at line 64, and continuing on to column 9, line 17, which shells can be comprised, for example, of polyurethanes, polyurea, epoxy resin, polyether resins such as polyphenylene oxide or thioether resin, or mixtures thereof; 4,937,167 relating to encapsulated toners with a diameter of less than 10 microns; and U.S. patents of background interest include U.S. Pat. Nos. 4,442,194; 4,465,755; 4,520,091; 4,590,142; 4,610,945; 4,642,281; 4,740,443 and 4,803,144.
Interfacial polymerization processes are described in British Patent Publication 1,371,179, the disclosure of which is totally incorporated herein by reference, which publication illustrates a method of microencapsulation based on in situ interfacial condensation polymerization. Moreover, there are disclosed in U.S. Pat. No. 4,407,922, the disclosure of which is totally incorporated herein by reference, interfacial polymerization processes for pressure sensitive toner compositions comprised of a blend of two immiscible polymers selected from the group consisting of certain polymers as a hard component, and polyoctadecylvinylether-co-maleic anhydride as a soft component.
Other prior art includes U.S. Pat. No. 4,520,091, the disclosure of which is totally incorporated herein by reference, which illustrates an encapsulated toner material wherein the shell can be formed by reacting a compound having an isocyanate with a polyamide, reference column 4, lines 30 to 61, and column 5, line 19; and U.S. Pat. No. 3,900,669 illustrating a pressure sensitive recording sheet comprising a microcapsule with polyurea walls, and wherein polymethylene polyphenyl isocyanate can be reacted with a polyamide to produce the shell, see column 4, line 34.
Illustrated in U.S. Pat. No. 4,758,506 (D/84024), the disclosure of which is totally incorporated herein by reference, are single component cold pressure fixable toner compositions, wherein the shell selected can be prepared by an interfacial polymerization process.
There is a need for colored encapsulated toners which display low minimum fusing temperatures of from about 100.degree. C. to about 120.degree. C., wide fusing latitude, can be formed in fine particle sizes such as from about 0.5 to 7 microns, have nonblocking tendencies, and with heat-fusible polyurethane shells with softening points of from about 80.degree. C. to about 120.degree. C., of high projection efficiency on a transparency such as from about 60 to about 95 percent transmittance, and of stable triboelectricity properties including substantially complete passivation. These and other needs are accomplished with the colored encapsulated toners and process thereof of the present invention. More specifically, thus with the toners of the present invention, the toner properties can in many instances be tailored to certain specifications. Additionally, complete or substantial passivation of the triboelectric charging effects of the colorants is accomplished, and smaller toner particle sizes of from about 2 microns to about 7 microns with narrow size distribution can be achieved without conventional classification techniques. Also, the toners of the present invention do not block or agglomerate over an extended period of time, for example up to six months, in embodiments.